Anthrax, a common disease in herbivores, is caused by the bacterium Bacillus anthracis. When faced with environmental stress and lack of nutrients, this Gram-positive bacterium converts to a hardy, dormant stage in the form of a spore. This spore can survive for decades in the soil, as well as in tissues of animal carcasses (e.g., cattle). In rare cases, these spores can become aerosolized during the processing of animal products, such as those used in textiles or meat by-products.
 There are three major routes of naturally-acquired anthrax infection: (1) the cutaneous form (most common); (2) gastrointestinal (from ingestion of microorganisms in contaminated meat, for example); and (3) inhalation anthrax. The third form is of most interest as anthrax spores can be readily used in biological weapons. Furthermore, anthrax is a very significant threat due to the relative ease of isolating, growing, and disseminating the bacterial spores. During the weaponization process, anthrax bacteria may also be further genetically modified to become antibiotic resistant. Anthrax spores can be weaponized in two basic forms: dried powder or liquid slurry. Spray tanks or munitions could deliver anthrax spores in point or line source release. While it is difficult to precisely define the median infectious dose (ID50) for anthrax spores, extrapolation from animal data indicates that a few thousand spores are necessary to infect humans through the inhaled route. Virulent anthrax bacteria form a capsule that is resistant to the body’s defense system, while excreting a toxin complex that is responsible for the disease process that follows infection. In the early stages, the disease may cause fever, cough, headache, or a similar constellation of flu-like symptoms lasting hours to a few days. The following stage may involve a rapid deterioration, including difficulty in breathing, high fever, and shock. At this point, even with medical intervention, death can follow quickly.
Anthrax is not known to be communicable from person-to-person, and therefore patients infected with anthrax do not require isolation. An FDA-licensed vaccine, based on the Protective Antigen (PA) portion of the anthrax toxin complex, is available to US Department of Defense personnel (mostly for active duty services) and is considered to be safe and effective against inhalation anthrax. |
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